Three-wire telephone system.



o. WINSTON.

THREE WIRE TELEPHONE SYSTEM.

APPLICATION FILED MAR. 12, 1906.

Patented Jan. V5, 1909.

@im mgl-5 j UNITED STATES' PATENT GFFICE. CHARLES s. wnvsron, orCHICAGO, ILLINOIS, sseivo To KELLOGG SwI'roHnoARn a SUPPLY COMPANY, orCHICAGO, ILLINOIS, A CORPORATION or ILLINOIS.

Specification of Letters` Patent. i

'Patented Jan. 5, 1909.

Application filed March 12, 1906. Serial No. 305,435.

l To all whom 'it 'may concern:

, telephone systems of the three-wire' type as distinguished fromsystems employing only two conductors in the mulit le switchboardsection of the lines. ln suci two-wire systems it is necessary to use aart of the talking circuit for the purpose o testing the idle or busycondition of the lines', and for signal ing purposes between thesubstations andthe central office. In three-wire systems an additionalconductor is. provided for testing and signaling purposes, vso thatthese func-- tions may be performed entirely independent of the talkingcircuit. i

'Ihe objects of niy invention are to provide a system of the latterclass that will be simple in Operation and inexpensive to install andone that will be free from possible voice current shunts other thanthose necessary to furnish the energy to the-lines for conversation, andfrom impedance in the talking circuit, whereby a high degree ofefficiency is obtained.

My invention is illustrated in the accompanying drawing in which theligure is a diagram showing twosubscribers lines and a l central oiiiceequipment for connecting the lines for conversation.

Referring to the drawing, two subscribers stations 1 and 2 are shownconnected with the central oifice'by means of line conductors 3` and 4.I have indicated a common battery substation outfit at the subscribersstations Consisting of the call bell 5 and condenser 6 in a permanentbridgeof theline conductors, and a transmitter 7 and receiver 8 yin abridge of Said conductors normally open atthe switch hook 9.

At the central oflice the limbs of the telephone lines terminate in thewindings 10 and 11 of a line relay 12, the winding 10 being connectedwith the non-grounded pole of the central olice battery 13 by-means ofconductors 14: and 15, and the coil 11 being connected to ground throughthe conductor 16 and the normallyeclosed contacts 17 of the y cutoffrelay 1S. A line lamp 19 is connected between the conductor 15 andground through normally-open contacts of the line relay 12 and thenormally-closed contacts 20 of the cut-off relay 18. The winding ofthecut-oiil relay is connected between ground and the testing terminal 21of the answering jack, said terminal and the tip and sleeve springs 22and 23 of the jacks being multipled at the dilierent sections oftheswitchboard.

The operators cord circuit consists of a tip strand 24 having aninterposed, condenser 25 and a sleeve strand 26 having an interposedcondenser 27. A Supervisory signal 28 is provided for the answering sideOfthe cord circuit, said signal being connected with the opposite polesof the battery 13 by means of conductors 29 and 30, and having thecontinuity of its circuit normally 'open at the front contact ofysupervisory relay 31 and normally closed at the lback contact of thesupervisory relay 32. The relay 31 is connected between the non-groundedside of the battery 13 and the tllird contact of the plug by means of aconductory 33 and relay 32 is connected between the grounded pole ofsaid battery and the sleeve strand of the cord circuit. A supervisorysignal 34 is similarly connected with reference to battery 13 u on theopposite side of the cord circuit and Ihas the continuity of its circuitsimilarly con--` trolled by the normally-open contacts Of a supervisoryrelay 35, and the normally-closed contacts of a supervisory relay 36.The relay 35 has one side of its Winding connected with the non-groundedpole of battery 13, the othei` side thereof being connectedto the thirdcontact of the callingr plug by conductor 37, and the relay 36 isconnected between the grounded Side of the battery 1.3 and the sleeveStrand of the cord circuit. A' second pair ofnormally-closed contacts38. are provided for the su ervisory relay 35, the conv tact anvil ofsai pair being connected with the tertiary winding 39 ol the operators1nduction coil by means of conductor 40. The

operation of the supervisoryrelay 35 seversv the connection between theti strand and the tertiary Winding, and unites the normally-severed tipstrand of the cord circuit at the front contacts of said relay forconversation. Y

A listening key 40 is provided adapted bridge the operators telephone.across the cord circuit in the usual manner; the transmitter 41 and theprimary of the operator's induction coil 42may be supplied with currentby the battery' 13 or from anu Atable source. A. ringing generator 43 isadapted to be connected with the limbs of the telephone line by means ofa ringing key44 for the purpose of signaling the desired subscriber.

1n the operation of the system the subscriber at station 1, desiring toattract the attention of the operator, will remove his receiver from theswitch hook and close a path for current from the battery 1 3 overconductors 14 and 15, the winding 10 of the line relay 12, limbs 3 and 4of the telephone line including the substation apparatus, winding 11 ofthe line relay, conductor 16 and contact 17of the cut-oltrelay 18 ktoground. 'lhe line relay will attract its armature, closing the circuitof the line signal 19 from conductor 15 to groundl through thenormallyclosed contacts 20 of the cutoft1 relay. Upon noticing thesignal the operator will raise the plug of the cord circuit and insertthe same 1n the answering jack of the calling line. Upon the insertionof the plug a path for current will be closed through the winding of thesupervisory relay 31, conductor 33, testing terminal 21, and the windingof the cut-ori' relay to ground. Both relays in this path will beenergized, the cut-ofirelay opening the circuit of the line lam 19 atits normally-closed contacts 20 an removing the round connection fromthe sleeve side of the ine at its normally-closed contacts 17. 'lherelay 31 will close the circuit of the supervisory signal 28 at thenormally-open contacts of said relay. lhe supervisory signal 28 wouldnot be lighted, however, due to the energization of the supervisoryrelay 32 inresponse to a ow of current over the telephone line; thisflow of current may. be traced from the battery 13 over conductors 14and 15, winding 10 of the line relay, line, conductor 3, the substationapparatus, line conductor 4, sleeve spring 23 of the jack and thecorresponding plug contact, sleeve strand 26 of the cord circuit, andthe winding of said relayl to batter It will be seen, therefore,

that the signa 28 will remain dark-duringconversation, due to the factthat the circuit of said signal is jointly controlled by the relays 31and 32, the former over a path local to the central olice, and thelatter over a ath including the substation apparatus and epending forits operation upon the position of the subscribers telephone receiver.Upon moving her listening key 40 and bridging her telephone set acrossthe cord circuit the o erator would be in communication with t e callingsubscriber. Upon learning the number of the line wanted itsconditionwould be tested in theusual manner by touching the tip of theplug to the testing terminal of the line wanted.` If a connectionexisted with the line at another position of the switchboard. thetesting terminals throughout the multiple of that line would be raisedto a potential above that of ground, due to the flow of current throughthe terminal at said position, 'to operate the cut-0E relay. Upontouching the ti of her plug to a multiple testing termina of a 'busyline a flow of current would result from the test rin over the tipstrand of the cord circuit, conductor 40, through the tertiary winding39 of the operators induction coil to ground. This flow of current wouldproduce an inductive click in the operatorshead receiver, notifying herof the busy condition of the line. lfinding the line idle the o eratorwould insert the plug in `the jack of t e line wanted. On the insertionof the plug current would ow through the supervisory relay 35, and thecut-oil relay 18, as described with reference to the answering side ofthe cord circuit. The operation of the cut-oil'I relay would open thecircuit of the line signal 19 at the normallyclosed contacts 20 of saidrelay and remove the ground from the sleeve side of the telephone lineat its normally-closed contacts 17 preventing the operation of the linerelay 1.2. '1`he operation of the supervisory relay 35 closes thecircuit of the supervisory lamp 34 at the normally-open contacts of saidrelay and severs the connection'between the tip strand of the cordcircuit and the tertiary winding of the operators induction coil at itsnormally-closed contacts, unit-ing vthe normally-severed parts of saidstrand for conversation. Due to the fact that the called subscriberstelephone was upon its hook no flow of 'current would result through thesupervisory relay 36 and the supervisory lamp 34 would be lighted toindicate this fact to the operator. The. operator would then throw herringing/key 44 to signal the subscriber, the path for ringing currentbeing -from the generator 43 over the sleeve contacts 'of the plug andjack, line conductor 4, substation ringing ap aratus, line conductor 3,ti strand of the p ug and jack, and back to t e generator through thegrounded contact of the ringing key. Upon the response of the calledsubscriber supe'rvisoryrelay 36 would be energized to extinguish thelamp 34 over a path including conductors 14 and 15, winding 10 of theline relay, line conductors 3 and 4 including the substation apparatus,the sleeve strand of the cord circuit and the winding ofthe supervisoryrelay 36 to battery. The subscribers would then be in communication, thetalking currents being propagated from one line'v to the other throughthe .interposed condensers 25 and 27 in the strands of the cord circuit.Either subscriber placing his'receiver upon the hook at the terminationof the conversation would denergiz'e the corresponding supervisoryrelay32 .or 36, permitting the armatures of said re ays to drop back andlight the associated supervisory signal to inform the"`operator that theconversation had terminated. U on withdrawing the plugs from the jacks'al parts of the system would be restored to normal condition.

- lWhat I claim as new and desire to secure by Letters Patent is:.

1. In a telephone system, the combination with atelephone line, of acord circuit for I making connection therewith for conversacircuitjointly control-led by the contacts of f said supervisory relays,substantially as described. l

2v. In a telephone system, the combination with a telephoneline, oi acord circuit for making connection therewith for conversa- `tion, athird conduct-cr at the central oiiice isolated from the talkingcircuit,` a cutott` relay and a supervisory relay in said thirdconductor, a line relay permanently con nected with the line, a sourceof current, a'

` second supervisory relay connected between said source and the sleevestrand of the cord circuit, a'nd a supervisory signal having its circuitnormally open at the contacts of said supervisory relay associated withsaid third conductor and normally closed at the con tacts of said lastmentioned supervisory relay, substantially as described. l

3. `In a telephone system, the combination with a telephone line, oi acord circuit for making connect-ion therewith for conversation, a thirdconductor at the central otlice isolated trom the talking circuit, acut-eti relay and a supervisory relay insaid third conductor, aline.relay having two windings, one permanently connected with each lineconductor, and a line signal having its circuit completed through thecontacts'o'f said line and cut-oit rel ys, a source oi' current, asecond supervisory relayconnected between said source and the sleeve.strand of the cord circuit, and a supervisory signal having its circuitnormally open at the contacts of said supervisory relay associated withsaid third conductor, said relay being in a circuit local to the centraloilice, and normally closed at the contacts of said? last mentionedrelay, said relay being in the path of current to the substation,substantially as described.

4. In a' telephone system, the combination with a telephone line, of acord circuit for" p. making connect-ion therewith for conversation, athird conductor at the centralotlice isolated Vfrom the talking circuit,a cut-oit` relay and a supervisory relay i-nsaid third conductor, a linerelay having two windings, one permanently connected with each lineconductor, aline signal having its circuit completed through thecontacts'of both said rela'-'s, a source of current, a second superevisory relay connected between said source and the sleeve strand of thecord circuit, said second supervisory relay being substituted in theline for one of the windings oi said line relay when a` connection isestablished for conversation, and a supervisory signal having itscircuit normally open at the contacts oi said supervisory relayassociated with said third conductor, vand normally closed at thecontacts of said last-mentioned supervisory relay, substantiallyasdescribed.

5. In a telephone system, the combination with a telephone line, oiacord circuit for connecting therewithfa third conductor at the centralotlice, .a cut-oli relay anda supervisory relay in. said thirdconductor, a line relay permanently connected with the line, a source ofcurrent, a second supervisory relay 'connected between said source and astrand ot the cord circuit, and a supervisory circuit jointly controlledby the contacts of said supervisory relays, substantially as described.

'7 In-a telephone system, the combination ywith-a telephone line, oi' acordy circuit connected therewith, a third conductor isolated from thetalking circuit, a cut-0R relay and a supervisory relay in said thirdconductor, a source of current, a line. relay with its -windingVpermanently connected between a limb ot' the line and a pole of saidsource, a second supervisory relay connected between the ot er pole oi'said source and a strand of the cordcircuit, and a supervisory signalhaving itscircuit jointly controlled by the contacts of said supervisoryrelays, substantially as described. f

8. In a telephone system, the combination fwith a telephone line, of acord circuitconnected therewith, 4a third conductor isolated frornt-hecord circuit, a supervisory relay in aid third conductor, a source oicurrent, a

second supervisory relay connected between isc the other pole of saidsource and the strand and State of illinois, in the presence of two ofsaid cord circuit connecting with the other witnesses.

limb of the telephone line', and a supervisory T signal having itscircuit jointly controlled by CHARLES S' NI-ASTON' 5 the contacts ofseid supervisory relays, sub- 'Witnessesny stantiall as described. f C.B. CAMP,-

Signetl7 by me at Chicago, county of Cook, (1x0. BRADBURY-

